1. Technical Field
The invention relates to a method of determining the position of a surface. More particularly, the invention relates to making such determination in a system of the type wherein a light beam is directed toward the surface and and image of the beam is detected through a lens arrangement. The invention further relates to apparatus for implementing the said method.
2. Discussion of the Prior Art
A method of the kind specified is known from German OS No. 21 40 939, according to which a body is placed into the parallel raypath or beam of a lens in the focal point of which a light source is arranged. The outside diameter of this lens is greater than the diameter of the body to be tested so that the body surface in every case forms a shadow within the parallel ray beam. The rays which remain unobstructed on either side of this radiation shadow impinge, for example, on a photodiode line scanning camera with about 1000 photoelements. In this manner one can ascertain the diameter of the body as well as its position within the beam. At any rate, positional deviations of the body in a vertical or perpendicular direction relative to the direction of propagation of the parallel rays are ascertained by this method. By contrast, positional deviations of the body, and thus of its surface, are not detected if such positional deviations occur in the direction of propagation of the beam. Furthermore it is a prerequisite condition for the known method that the surface of the body must be fully irradiated and that, over and above this, the rays of the beam must be unobstructed on either side of the surface.